1. Field of the Invention
The present invention relates to welding machines and, more particularly, to welding controllers that control the operation of the welding machines and that can be easily reprogrammed to change the operation of the welding machine.
2. Background of the Invention
Known resistance welding machines are described, for example, in U.S. Pat. Nos. 4,985,612 and 5,808,885. These prior art welding machines are typically installed in automobile production lines or other assembly lines. A representative hardware architecture for such a known welding machines is shown in FIG. 2. Prior art welding controller 53 for controlling the welding machine may include a central processing unit (CPU) 53a, a memory having a PROM (xe2x80x9cprogrammable read only memoryxe2x80x9d) or EPROM (xe2x80x9cerasable programmable read only memoryxe2x80x9d) 53b and a RAM (random access memory) 53c, a switching element 53d such as a transistor or a thyristor, an input/output port (I/O) 53e, and a serial communications port (SIO) 53f. 
In such welding controller systems, programs and data are written into the EPROM 53b and sequential welding data are written into RAM 53C. The EPROM 53b generally contains a sequential welding program, a current control program and a communications program. The communications program operates to permit an operator to select the sequential welding program or to input sequential welding data. The sequential welding program permits the operator to change the sequential welding data. Sequential welding data includes the welding time, welding current, and other welding parameters, for the welding operation. The CPU 53a executes programs stored in EPROM 53b based upon the sequential welding data stored in RAM 53c. Further, CPU 53a executes the communications program to write sequential welding data into RAM 53c. The sequential welding data may be input into RAM 53c by an input device 54, as discussed below.
EPROM 53b usually must be erased using a physical process, such shining an ultraviolet light on EPROM 53b. Therefore, EPROM 53b must be physically removed from the welding controller 53 in order to change the programs or data stored in EPROM 53b. Further, new programs and data are written into the EPROM 53b in the following manner:
(1) Programs and data are first prepared using a computer 51 and the new programs and data are transferred to ROM writing device 52;
(2) EPROM 53b is placed in ROM writing device 52;
(3) The programs and data, which have been transferred to ROM writing device 52, are written into EPROM 53b; and
(4) EPROM 53b is placed in a socket within the welding controller 53. For example, EPROM 53b is inserted into a ROM socket of printed circuit board 59 that is disposed within a control box 60 as shown in FIG. 3.
The input device 54 is used to input sequential welding data and is connected to connector 54b of the welding controller 53 via a cable 54a. Input device 54 includes CPU 54c, a memory such as ROM 54d and RAM 54e, a keyboard 54f, a display 54g, and a serial communications port (SIO) 54h. The communications program may be executed, for example, using keyboard 54f. Based on the communications program, the sequential welding data input by the input device 54 is transferred to the welding controller 53 through the serial communications ports (SIO) 54h and 53f and is then written into the RAM 53c of the welding controller 53. In the alternative, the operator can manually input the sequential welding data using a touchscreen display 54g. 
When starting switch 59 is actuated, CPU 53a controls the welding machine based upon the programs stored in EPROM 53b and sequential welding data in RAM 53c. For example, CPU 53a moves welding electrodes 56 such that workpiece 57 is held between the electrodes 56 under pressure. Further, CPU 53a provides control signals to switching element 53d in order to control the welding current that is supplied to the electrodes 56 via a welding transformer 58.
Typically, welding specifications are changed or additional functions may be required after the welding machine has been installed on an automobile production line or other manufacturing environment. In addition, bugs may exist in the programs or data. In such cases, the programs or data in EPROM 53b must be rewritten. However, according to known welding controllers, in order to rewrite the programs or data in EPROM 53b, EPROM 53b attached to the printed board 59 must be physically removed and replaced with an EPROM having the new programs and data. Thus, in order to replace the EPROM 53b, the following operations are required: the power must be turned off, door 60a of control box 60 is opened, old EPROM 53b is removed, new EPROM 53b placed in the appropriate socket of printed circuit board 59, door 60a is closed, and the power is turned on again.
If a plurality of resistance welding machines (for example, usually about ten) have been installed in an automobile production line or other manufacturing environment, a corresponding number of welding controllers 53 are required to control each welding machine. In order to minimize floor space requirements for the welding control system, control box 60 may be installed in an awkward location and it may be difficult to open and close door 60a. Because of this, the printed circuit board 59 may be disposed near other devices, such as the welding transformer, welding gun or robot controller. In such cases, replacement of EPROM 53b of welding controller 53 may be quite difficult due to space restraints and it may take a long time to replace EPROM 53b. Further, when replacing EPROM 53b, other ICs on the printed circuit board 59 may be electrostatically destroyed or a pin of EPROM 53b may be damaged. Finally, if the factory does not have ROM writing device 52 in order to prepare new EPROM 53b, new EPROM 53b must be prepared elsewhere and then delivered to the factory.
It is, accordingly, an object of the present teaching to provide welding controllers that overcome some or all of the problems of the prior art.
According to one aspect of the present teachings, a write program for writing programs or data into a first memory is stored in a second memory. When welding operation programs or sequential welding data is input into the CPU from external equipment, the CPU executes the write program to write the inputted program or data into the first memory. Thus, welding operation programs or sequential welding data can be easily written into the first memory from an external source without replacing the first memory. Preferably, the CPU may execute a write operation when a predetermined writing command is input from the external source.
According to another aspect of the present teachings, the CPU may control the welding machine when a mode select switch is set for a welding mode. In addition, the CPU may execute a write operation when the mode select switch is set for a writing mode. Therefore, even when the welding mode switch is set to the welding mode and a predetermined writing command is input into the CPU from the external source, the CPU preferably may execute the write operation. In this case, welding operation programs or sequential welding data can be written into the first memory from the external source at any time, irrespective of the selected mode. Further, if a predetermined writing command is input into the CPU from the external source while the CPU is executing a program to control the welding operation, the CPU may preferably complete the welding control instructions before executing the write operation. As a result, the occurrence of welding defects can be prevented or reduced.
In another aspect of the present teachings, the CPU may determine whether welding operation programs or data have been properly written into the first memory. Thus, any improperly written program or sequential welding data can be re-written into the first memory and programs or sequential welding data can be reliably written into the first memory. Preferably, the CPU verifies the written programs and data in the first memory using a parity check or checksum program. In this case, the CPU can easily determine whether programs or data has been properly written into the first memory.
Additional objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.
The above and other preferred features of the invention, including various novel details of implementation and combination of elements will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular methods and circuits embodying the invention are shown by way of illustration only and not as limitations of the invention. As will be understood by those skilled in the art, the principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.